This invention relates to an improvement in a pneumatic tire provided with reinforcing layers in the beads, and more particularly to a pneumatic tire having improved casing rigidity (lateral rigidity of beads) which enables the steering stability of a vehicle to be improved.
As the performance of a vehicle has been improved to a higher level, a pneumatic tire with further improved steering stability has been demanded. To meet this demand, the casing rigidity-improving techniques have been used in practice for increasing the cornering force, by providing in addition to a bead filler a reinforcing layer, which consists of organic fiber cords or metal cords covered with coating rubber of a hardness of around JIS Hs 55-60, in a bead of a tire in such a manner that the reinforcing layer extends along a turnup portion of a carcass layer.
However, it has come to be demanded in recent years that the performance of a pneumatic tire with respect to the steering stability of a vehicle be further improved, and it has been proven that providing a reinforcing layer only in a bead as mentioned above serves to improve the lateral rigidity of the bead (widthwise rigidity of the tire) to only a limited extent. In order to further improve the performance of a pneumatic tire, an attempt to provide a multilayer reinforcing member in a bead has also been made but this causes the weight of the tire to increase, and, moreover, the number of manufacturing steps and the manufacturing cost increase. Therefore, providing a multilayer reinforcing member does not constitute a substantial solution to the problem.